1 /* 2 * Copyright (c) 2020, 2021, Amazon.com, Inc. and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #include "precompiled.hpp" 26 #include "gc/shenandoah/shenandoahCardTable.hpp" 27 #include "gc/shenandoah/shenandoahHeap.inline.hpp" 28 #include "gc/shenandoah/shenandoahUtils.hpp" 29 30 void ShenandoahCardTable::initialize() { 31 CardTable::initialize(); 32 _write_byte_map = _byte_map; 33 _write_byte_map_base = _byte_map_base; 34 const size_t rs_align = _page_size == (size_t) os::vm_page_size() ? 0 : 35 MAX2(_page_size, (size_t) os::vm_allocation_granularity()); 36 37 ReservedSpace heap_rs(_byte_map_size, rs_align, _page_size); 38 if (!heap_rs.is_reserved()) { 39 vm_exit_during_initialization("Could not reserve enough space for second copy of card marking array"); 40 } 41 os::commit_memory_or_exit(heap_rs.base(), _byte_map_size, rs_align, false, "Cannot commit memory for second copy of card table"); 42 43 HeapWord* low_bound = _whole_heap.start(); 44 _read_byte_map = (CardValue*) heap_rs.base(); 45 _read_byte_map_base = _read_byte_map - (uintptr_t(low_bound) >> card_shift()); 46 47 log_trace(gc, barrier)("ShenandoahCardTable::ShenandoahCardTable: "); 48 log_trace(gc, barrier)(" &_read_byte_map[0]: " INTPTR_FORMAT " &_read_byte_map[_last_valid_index]: " INTPTR_FORMAT, 49 p2i(&_read_byte_map[0]), p2i(&_read_byte_map[last_valid_index()])); 50 log_trace(gc, barrier)(" _read_byte_map_base: " INTPTR_FORMAT, p2i(_read_byte_map_base)); 51 52 // TODO: As currently implemented, we do not swap pointers between _read_byte_map and _write_byte_map 53 // because the mutator write barrier hard codes the address of the _write_byte_map_base. Instead, 54 // the current implementation simply copies contents of _write_byte_map onto _read_byte_map and cleans 55 // the entirety of _write_byte_map at the init_mark safepoint. 56 // 57 // If we choose to modify the mutator write barrier so that we can swap _read_byte_map_base and 58 // _write_byte_map_base pointers, we may also have to figure out certain details about how the 59 // _guard_region is implemented so that we can replicate the read and write versions of this region. 60 // 61 // Alternatively, we may switch to a SATB-based write barrier and replace the direct card-marking 62 // remembered set with something entirely different. 63 64 resize_covered_region(_whole_heap); 65 } 66 67 bool ShenandoahCardTable::is_in_young(const void* obj) const { 68 return ShenandoahHeap::heap()->is_in_young(obj); 69 } 70 71 bool ShenandoahCardTable::is_dirty(MemRegion mr) { 72 for (size_t i = index_for(mr.start()); i <= index_for(mr.end() - 1); i++) { 73 CardValue* byte = byte_for_index(i); 74 if (*byte == CardTable::dirty_card_val()) { 75 return true; 76 } 77 } 78 return false; 79 } 80 81 size_t ShenandoahCardTable::last_valid_index() { 82 return CardTable::last_valid_index(); 83 } 84 85 void ShenandoahCardTable::clear() { 86 CardTable::clear(_whole_heap); 87 } 88 89 // TODO: This service is not currently used because we are not able to swap _read_byte_map_base and 90 // _write_byte_map_base pointers. If we were able to do so, we would invoke clear_read_table "immediately" 91 // following the end of concurrent remembered set scanning so that this read card table would be ready 92 // to serve as the new write card table at the time these pointer values were next swapped. 93 // 94 // In the current implementation, the write-table is cleared immediately after its contents is copied to 95 // the read table, obviating the need for this service. 96 void ShenandoahCardTable::clear_read_table() { 97 for (size_t i = 0; i < _byte_map_size; i++) { 98 _read_byte_map[i] = clean_card; 99 } 100 } 101 102 // TODO: This service is not currently used because the mutator write barrier implementation hard codes the 103 // location of the _write_byte_may_base. If we change the mutator's write barrier implementation, then we 104 // may use this service to exchange the roles of the read-card-table and write-card-table. 105 void ShenandoahCardTable::swap_card_tables() { 106 shenandoah_assert_safepoint(); 107 108 CardValue* save_value = _read_byte_map; 109 _read_byte_map = _write_byte_map; 110 _write_byte_map = save_value; 111 112 save_value = _read_byte_map_base; 113 _read_byte_map_base = _write_byte_map_base; 114 _write_byte_map_base = save_value; 115 116 // update the superclass instance variables 117 _byte_map = _write_byte_map; 118 _byte_map_base = _write_byte_map_base; 119 }